Sir William bought the Rivington estate in 1900. Following a law-suit, Liverpool Corporation bought the majority of the estate with Lever retaining the 45 acre site.

Lever commissioned Mawson to design the gardens. They had met a few years earlier when Mawson had written to Lever, asking for a donation towards the cost of a carved folding screen he had designed for the Church at Hest Bank. Enclosing a cheque, Lever replied: ‘now that you have had the courage to ask me for a subscription, may I be so bold as to ask you to come and advise me upon the improvement of my garden at Thornton Manor? I have wanted to consult you for the last two years, but all my friends warned me that it would be useless, as you never worked for anyone holding less social rank than a Duke, whereas I am only a poor and indigent soap-maker….’

Lever chose to erect a large prefabricated wooden structure on the site. Known as Roynton Cottage, it was destroyed in 1913 in an arson attack by the suffragette Edith Rigby. Ironically, Lever was a supporter of the Movement. Lever’s friend, Jonathan Simpson designed the replacement. Built of stone, it was known as The Bungalow. With Pergolas, a courtyard and an aviary, a second floor was added in 1923. It overlooked the Orchestral lawn with its sundial – supposedly where Lever proposed to his wife.

Mawson wrote about the design in his work, ‘The Art and Craft of Garden Making’: ‘It is an especial pleasure to describe the grounds to Roynton Cottage, the mountain home of the late Viscount Leverhulme, for, of all the gardens laid out by him, there have been few which have provided such scope for originality and at the same time such an incentive to grace the unique site and its surroundings, an incentive which was heightened and enlarged by the exceptionally sympathetic interest of the late proprietor.’

Many doubted whether plants would grow on the exposed site and Mawson enjoyed proving them wrong. He wrote: ‘[we] planted thousands of rhododendrons, including choice hybrids and many interesting species of Alpine varieties ….and every other peat-loving shrub, together with berberis, cotoneaster, hollies….many of which are rarely found in gardens. It was a bold enterprise, but we planted liberally, taking risks which in the event were abundantly justified – so much so that none of the places I have planted for the same client in Cheshire, Hampstead, or the Isle of Lewis can bear comparison with this.’ Sadly, all Rhododendron were removed from the gardens in 2006 after Phytophthora Ramorum Disease – Sudden Oak Death – was found at the site.

Mawson was against using ‘artificiality’ at Rivington. He wrote: ‘Seeing that all the surroundings of the new garden were rugged and wild, therefore, in order to harmonize with them and fall properly into place and express their spirit, it must not only receive exceptional breadth of treatment at every point, but must, in its architectural details, be free from artificiality.’

Mawson also developed a ravine from a stream: ‘At another place, the presence of a tiny mountain rill has been taken advantage of to form a rocky waterfall with a series of large pools below.’

It seems however, that Mawson did use the artificial rock called pulhamite on creating some of the structures on the site including the Japanese Garden.

After Lever’s death, The Bungalow and grounds were purchased by the Bolton brewer, John Magee. He opened the gardens to the public and converted part of the Great Lawn into a tennis court. After his death, the property was offered to Bolton Council but they turned it down.

Liverpool Corporation bought Rivington in 1939 and during the War, the site was requisitioned by the army. The Bungalow was badly damaged and was demolished in 1948. The garden fell into disrepair and in 1967, the Corporation threatened to demolish the remaining structures. But a public outcry led to the site being saved.

By 1974, the gardens had passed to the North West Water Authority and after privatisation to United Utilities. Again, the garden structures were threatened with demolition but were saved by Chorley Council who gave them listed building status.

Rivington Heritage Trust was formed by United Utilities in 1997.  A grant of £3.4 million from the Heritage Lottery Fund enabled the Trust to conserve and repair the Rivington Terraced Gardens and the remaining Grade II listed structures.

In 2016, a lease of 50 years was agreed by United Utilities to the Rivington Heritage Trust.